The sine-bar is used for angular measurements or for the location of work at given angles, as for example in measuring or checking angles with accuracy using precision gage-blocks selected for whatever dimension is required in obtaining a given angle. Precision gage-blocks are used in sets comprising a specific number of blocks of different sizes determined mathematically so that particular heights can be obtained by combining selected blocks, two or more blocks being combined by "wringing" them together with a swivelling motion causing them to adhere one to the other. When combining blocks in this conventional way for a given dimension, the object is to use as few blocks as possible, the procedure being based upon successive elimination of the right hand digit of the desired dimension. For example, the combined blocks measuring 0.1002+0.124+0.450+3.00 equals 3.6742 inches. An accurate surface plate or master flat is always used in conjunction with a primary sine-bar in order to form the base from which the vertical measurements are made, with precision gage-blocks in English or Metric increments of measurement. A standard length for sine-bars is five inches (also ten inches) and there are tabulated constants that represent vertical heights H for setting a five inch sine-bar (also for ten inch bars) to the required angle. Assuming that the required angle is 31.degree. 20', the sine tables show that the height H should equal 2.6001 inches. Note that the constants in the sine tables equal five times the sine of angle: Thus the sine of 31.degree. 20' in the trigonometric function table is 0.52002, and 0.52002.times.5 equals 2.6001 inches. There are many such functions for the use of a sine-bar, such as finding and checking angles, measuring angles and tapers and to determine center distances etc. The aforesaid conventional use of gage-blocks is replaced by using direct displacement gage-blocks as they are disclosed and claimed in U.S. Pat. No. 4,389,785 issued to Goldsmith et al June 23, 1983, entitled SINE-BAR GAGE BLOCKS AND DIRECT READING MICROMETER ADJUSTMENT. The advantage of the direct displacement gage blocks is that the teadious reference to trig tables and the selection of numerous blocks is eliminated, thereby avoiding accident, mistake and resultant errors. With the present invention, conventional gage-blocks or said direct displacement gage-blocks can be employed in setting primary and secondary sine-bars at the required degree of angularity.
Sine-bars are precision devices for measuring angles accurately and to locate work at a desired angle to some true surface, preferably a surface plate or the like. Conventional sine-bars consist of a hardened ground and lapped steel bar which has accurately spaced cylindrical plugs of equal diameter attached to or near each end. The sine-bar usually has notched ends to receive the cylindrical plugs which are held firmly against angular faces of the notches, and so as to form a support projecting only from the bottom of the bar. The upper side of the usual sine-bar is flat and parallel to the axes of the two underlying plugs within very close limits. There are various forms of sine-bars and refinements carrying forward the sine-bar concept. In compound sine-plates, the work supporting secondary sine-plate has its own two plugs and employs the underlying primary sine-plate as a base. In any event, gage-blocks have been used for elevating these two sine-plates respectively, and it is an object of this invention to improve this situation by combining the primary and secondary sine-plates using two plugs common to these two sine-plates, for direct adjustment of both the primary and secondary sine-plates by means of direct displacement gage-blocks and/or by a direct reading micrometer adjustor for fine adjustment within the angularity of the first mentioned angular adjustment in degrees.
It is a general object of this invention to proivde a sine-bar which is variable in order to be adjusted within degrees, minutes and seconds, and to this end it is similar to compound sine-bars, in that it is characterized by primary and secondary sine bars or plates, each of which is individually set at an exact angle. However, compound sine-bar arrangements are cumbersome, and therefore it is an object of this invention to render primary and secondary sine-bars more compact and easy to use as a unit wherein common plugs are employed in combination with only two sine-plates, a primary sine-plate and a secondary sine-plate. In practice, there is one base plug and one altitude plug, and the two sine plates are combined with both plugs respectively.
Heretofore, primary and secondary sine-plates of compound sine-bars and the like have employed individual base plugs for each. It is an object of this invention to provide a single common base plug for combined primary and secondary sine bars or plates. With this invention the base plug functions both as a tangent support upon a surface plate or the like, and as a hinge between the primary and secondary sine-plate. It is also an object to provide a base plug that couples the primary and secondary sine plates together as a unit. And, it is still another object of this invention to provide anti-friction engagement of the base plug with the primary and secondary sine-plates and which eliminates line contact therewith.
Heretofore, primary and secondary sine-plates of compound sine-bars and the like have employed individual altitude plugs, or the equivalent, for each. It is an object of this invention to provide a single common altitude plug, for combined primary and secondary sine bars or plates. With this invention the altitude plug functions both as a tangent support upon one or more gage blocks or the like, and as a tangent support between the primary and secondary sine-plates. It is also an object to provide an altitude plug that accomodates the primary support gage blocks while simultaneously supporting the secondary sine-plate adjuster means as hereinafter described. And it is still another object of this invention to provide anti-friction engagement of the altitude plug with the adjuster means of the secondary sine-plate and which eliminates scrubbing line contact therewith.
Micrometers take various forms, comprised generally of two visible elements and namely a barrel and a thimble, the barrel operating on a screw having forty threads per inch so that one revolution moves the baarrel and thimble one fortieth of an inch. A feature is the relationship of calibrations on one element relative to an index line on the other element. In normal practice, the barrel is provided with a straight axially disposed index line stepped off incrementally in calibrations spaced 0.025 inch, and the thimble with an edge overlying said index line and calibrated circumferentially into twenty-five equal parts. Thus, each line on the thimble represents one thousandths of an inch, while each calibration line on the barrel represents twenty-five thousandths of an inch. Heretofore, 11.5 threads per inch has been used to provide for one degree of thimble travel per turn, and this resolution can be employed here if so desired. However, it is an object of this invention to increase resolution and to provide an inside micrometer that reads in plus or minus degree of angle on the barrel as related to a sine-bar of which it is made a part, with degrees, minutes and seconds of angle being available as easily readable scaled indicia on the thimble. Accordingly, a high resolution screw having 45.84 threads per inch is provided so that one revolution moves the thimble one fortysixth of an inch, or 0.0218 inch. Characteristically therefore, we now provide a thimble that moves 15 minutes per revolution and which requires four turns or revolutions to move 60 minutes or a full degree. A feature of this thread pitch determination is that the thimble is of substantial diameter and is calibrated in 15 and 71/2 second increments, or closer if desired, for greater resolution in angular settings. Reference is made to U.S. Pat. No. 4,238,888 issued to Goldsmith Dec. 16, 1980, entitled DIRECT READING MICROMETER FOR SINE-BAR ELEVATION wherein a micrometer of this typs employing a vernier scale is disclosed and which can be utilized here to provide precision second readings.